Triaxial compression test apparatus

ABSTRACT

A high-speed triaxial compression test apparatus having a hollow rectangular frame with a central rectangular test cavity for containing a test sample and a rectangular opening to the test cavity in each side of the frame containing a removable pressurizing module having an inner movable pressure wall, such as a flexible diaphragm, which is pressurized through an inlet port in the module to exert a compression load on the test sample along the respective cavity axes, and transducers for generating signals representing the pressure on and displacement of the pressure wall. The primary application of the apparatus is testing soil and rock samples and other natural and fabricated materials to obtain data concerning their mechanical properties.

United States Patent 11 1 Shaw 1 1 Apr. 24,1973

[ TRIAXIAL COMPRESSION TEST APPARATUS Primary Examiner-Jerry W. Nyracle[75] Inventor: Garrett D. Shaw, Rolling Hills, Attorney Dan.lel AndersonDonald Nyhagen Calif. and Jerry A. Dmardo [73] Assignee: TRW lnc.,Redondo Beach, Calif. [57] ABSTRACT Filedi 1970 A high-speed triaxialcompression test apparatus hav- [21] Appl Na; 99,356 ing a hollowrectangular frame with a central rectangular test cavity for containinga test sample and a rectangular opening to the test cavity in each sideof [52] 11.8. CI ..73/94, 73/503 the frame Containing a removablepressurizi'ng module [5 I] hit. Cl. G0ln 3,08 having an inner movablepressure n Such as a flexi Fleld of Search ble p g which i pressurizedthrough an inlet port in the module to exert a compression load on the[5 6] 7 References Cited test sample along the respective cavity axes,and trans- UNTTED STATES PATENTS ducers for generating signalsrepresenting the pressure on and displacement of the pressure wall. Theprimary i application of the apparatus is testing soil and rock atsamples and other natural and fabricated materials to FOREIGN PATENTS ORAPPLICATIONS obtain data concerning their mechanical properties.

21 1,849 2/1968 U.S.S.R. ..73/94 1 Claim, 3 Drawing Figures 42 24 4e 2 2i8 26 44 4O 2O 2 8 \8 J t 36 u I u 38 42 34 l l 24 24 4o 50 4O 2 2PATENTEU APR 24 I975 INVENTOR.

Garret? D. Show ATTORNEY TRIAXIAL COMPRESSION TEST APPARATUS BACKGROUNDOF THE INVENTION 1. Field of the Invention This invention relatesgenerally to the field of materials testing and more particularly to ahigh-speed, triaxial compression test apparatus for soil, rock and othernatural and fabricated materials.

2. Prior Art As will appear from the ensuing description, the presentcompression test apparatus may be employed to test a wide variety ofnatural and fabricated materials. However, the primary application ofthe apparatus is testing soil and rock samples. For this reason, theinvention will be described in connection with this particularapplication.

A knowledge of the constitutive or mechanical properties of soil androck is important if not essential to the study and/or design of relatedstructures, such as structures to be constructed on or within naturalsoil or rock formations, as well as to the study of natural and nuclearor other explosively induced shock phenomena. The prior art is repletewith a vast assortment of test apparatus for determining such materialproperties. By way of example, a few of the prior art patents disclosingtest apparatus for the purpose described are U.S. Pat. Nos. 2,810,289;2,811,038; 3,119,341; 3,216,242; 3,423,994; 3,423,995; 3,443,423; and3,448,608.

Generally speaking, test apparatus of the character described comprisesa container with a cavity for receiving a sample of the soil or rock tobe tested, means for subjecting the sample to a compression load, andmeans for measuring the compaction and/or other parameters of the samplewhich are affected by the applied force. In some test apparatus, thetest force or loading is applied along a single axis. The Karol patent,U.S. Pat. No. 2,811,038, discloses a single axis test apparatus of thiskind. In other test apparatus, such as that disclosed in the Scott etal. U.S. Pat. No. 3,423,995, a loading force is applied to the testsample along each of three mutually perpendicular axes.

SUMMARY OF THE INVENTION The present invention provides an improvedtriaxial compression test apparatus of the general type disclosed in thelatter Scott U.S. Pat. No. 3,423,995. The present test apparatus has ahollow, one-piece rectangular frame which is typically cubic in shapeand machined from a single block of metal. Within the frame is a centralrectangular void. Each side of the frame contains a rectangular openingwhich is centered on the respective axis of and has the samecross-section as the void.

Removably mounted within each frame side opening is a pressurizingmodule having a rectangular body plate which fits closely within theopening. Means are provided for releasably securing the plate within theopening. At the inner side of the plate is a movable pressure wall whichdefines with the plate a pressure chamber. In the disclosed embodiments,this pressure wall is a rectangular diaphragm perimetrically sealed tothe edges of the module plate. The diaphragms of the six modulestogether define a rectangular test cavity for receiving a sample of thematerial to be tested.

Each module of the apparatus has a port communicating with therespective pressure chamber through which the chamber may be pressurizedto apply a compression load through the pressure wall to the test samplealong the respective test cavity axis. Also embodied in each module aretransducers for producing signals representing the applied pressure andthe displacement of the pressure wall. The modules may be selectivelypressurized to apply a compression load to any one or more selectedsides of the test sample.

Primary advantages of the apparatus reside in its ease of test sampleplacement within the test cavity; improved sealing and uniform loadingcapability; reduced face plane bending and other distortion affectingthe test results; and high speed cycling or shock loading capability.These advantages stem primarily from the unique unitary frame andseparate pressurizing module arrangement of the test apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is an exploded perspective view partly in secv DESCRIPTION OF THEPREFERRED EMBODIMENTS The compression test apparatus 10 illustrated inFIGS. I and 2 has a hollow, one-piece rectangular frame 12 which ispreferably machined from a single block of metal. Within the frame is acentral rectangular void. Each side of the frame 12 has a rectangularopening 18 to the central void. In the particular inventive embodimentshown, the frame 12 and its central void are cubic in shape and eachframe side opening 18 has an inner square cross-section matching that ofthe void. The configuration of the frame 12 is such that the frame hasintegral rectangular load bearing sections 20 extending between andjoining the opposite parallel frame sides through which forces aretransmitted between the sides.

Removably mounted within each frame side opening 18 is a self-containedpressurizing insert of module 22. The several modules are identical sothat a description of one will suffice for all. Each module has arectangular body plate 24 which is sized to fit closely within therespective frame opening. In the particular embodiment under discussion,the inner ends of the frame opening and module plate are reduced to formshouldcrs 26, 28 about the opening and plate which abut to position theplate in the opening. The inner end of each frame opening has the samecross-section as the central frame void. The module plate 24 isreleasably secured in its frame opening 18 by four hold-downs 30 whichengage over the four corners of the plate and are attached to the frame12 by screws 32.

At the inner side of the module plate 24 is a movable pressure wall 34in the form of a flexible diaphragm. Diaphragm 34 extends across theinner face of the plate and is perimetrically sealed to the plate aboutthe plate edges. In the particular embodiment shown, the diaphragm issealed to the plate by engagement of a perimetrical bead 36 about thediaphragm within a sealing groove 38 about the edges of the plate. Thediaphragm and plate define therebetween a pressure chamber 40.

Module plate 24 has a port 42 opening through its outer surface forconnection to a source of pressurizing fluid, such as hydraulic fluid.Port 42 communicates to the pressure chamber 40 through a number offluid passages 44. These passages open to the chamber 40 at a number ofpositions spaced about the chamber so as to permit rapid pressurizing ofthe chamber.

Each pressurizing module 22 also includes a pair of transducers 46, 48.Transducer 46 is a displacement transducer for producing an electricaloutput representing the displacement of the pressure wall as diaphragm34 from a given reference position, such as the position occupied by thediaphragm prior to the pressurizing of the pressure chamber 40 at thestart of a test. This transducer may comprise a proximity transducerwhich produces an electrical output proportional to the spacing betweenthe transducer and the diaphragm which, in this instance, will be ametal diaphragm or other diaphragm with a metallic member opposite thetransducer. Transducer 48 is a pressure transducer which is exposed tothefluid pressure in pressure chamber 40 and produces an electricaloutput representing the fluid pressure.

As noted earlier and shown in the drawings, each side opening 18 of theframe 12 contains a pressurizing module 22. Accordingly, there are apair of the modules along each of the three axes of the test cavity 14.The diaphragms 34 of the six modules together define and form the sixwalls of the rectangular test cavity 50.

In use of the. test apparatus 10, one or more of the pressurizingmodules 22 are removed to provide access to the test cavity 50, and thesoil, rock, or other material to be tested is placed in the cavity. Apressurizing fluid is then supplied to a selected one or more of themodules through their ports 42 to pressurize the correspondingpressure-chambers 40 and thereby urge the respective diaphragms 34inwardly against the test sample. Assuming all of the modules arepressurized, the sample is compressed between a pair of opposing wallsof the test cavity 50 along each of the three axes of the cavity. Inthis regard, it will be understood that the diaphragms are constructedof any suitable plastic material or other material which is capable ofyielding under the fluid pressure in the pressure chambers 40 to exertcompression loads on the test sample. During inward displacement of thediaphragms 34 under pressure, the adjacent diaphragms abut along thecorner edges of the test cavity 50 with the contacting surface portionsof the diaphragms disposed approximately in 45 planes bisecting therespective corner, such that the cavity is virtually devoid of any gapsat the corner edges.

During the sample loading cycle, the outputs of the several moduletransducers 46, 48 are monitored to obtain data from which may bedetermined the constitutive or mechanical properties of the test sample.The modules 22 may be pressurized according to any selectedpressure-time program ranging from relatively slow rate of change to arelatively high rate amounting essentially to impact loading of the testsample.

Moreover, the pressure-time program for the modules may be the same ordifferent depending upon the desired test conditions to be achieved.

The modified test apparatus 10a of FIG. 3 is identical to that justdescribed except for the configuration of the pressurizing modules 22aand their method of attachment to the frame 12a. Thus, each module 22ahas a rectangular body plate 244 with an inner rectangular plate portion24a which fits closely within the respec tive frame side opening 18a andis sealed to the module pressure wall or diaphragm 34a in the samemanner as in the test apparatus 10 and an outer rectangular plateportion 24a, which projects edgewise beyond the inner plate portion toform a mounting flange 24a, about the latter plate portion.

The mounting flange 22a, of each module 22a seats against the outer faceof the frame 12a about the respective frame side opening 18a. Themodules are secured to the frame by bolts 320 which extend through theflanges 24a of a pair of modules 22a at opposite sides of the frame andthrough the intervening comer load transmitting sections 200 of theframe. Thus, the bolts serve as tie rods which secure opposing parallelmodules to the frame. The crossing bolts are laterally offset such thatthey do not interfere with one another. According to the preferredpractice of the invention, the bolts 32a are initially tightened toprestress them in tension and thereby prestress the frame loadtransmitting sections 20a in compression. This prestressing of the framesections reduces deformation of the frame under load. The modifiedapparatus 10a is used in the same manner as the test apparatus 10.

The present test apparatus possesses several inherent advantages. Amongthe foremost of these advantages are:

l. Capability of much higher loading pressures than the existing testdevices.

2. The pressurizing modules are inherently capable of adequate sizing toaccommodate fluid passages of sufficient diameter and distribution toachieve short (high speed) loading cycles.

3. The frame configuration is inherently capable of sustaining highpressure loading due to the straight line tension load paths provided bythe frame corner sections.

4. The pressurizing modules are independent subassemblies which arealmost totally independent of one another with regard to theirdimensional tolerances and their diaphragms.

5. The module-to-frame seals are completely independent of the adjacentmodules.

6. The separate modules provide maximum ease of sample loading as wellas servicing.

lclaim:

l. A triaxial compression test apparatus comprising:

a hollow, one-piece rectangular frame having integral load bearingsections of substantially equal uniform cross-section extending alongthe frame edges between opposite parallel sides of the frame andpermanently integrally joined to one another at the frame corners overthe entire cross-section of each section so as to provide a frame devoidof separable joints, said frame containing a central rectangulartestcavity and a rectangular opening in each side of said frame on therespective axis of diaphram to said plate in fluid sealing relationtherewith to define between said diaphragm and said plate a'pressurechamber, and a port in said plate communicating with said chamberthrough which a pressure fluid may be introduced into said chamber tourge said diaphram against a test sample within said cavity; and

means releasably securing each module in its respective frame opening.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO.3,728,895

DATED 1 April 24, 1973 |NVENTOR(S) 1 Garrett D. Shaw It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Figure 2, top of module, numeral 22 needs arrow.

Signed and Bald this econd Day of new 1975 [SEAL] Arrest:

RUTH C. MASON C. IARSIIALI. DANN Arresting Officer CommissionerofParents and Trademarks

1. A triaxial compression test apparatus comprising: a hollow, one-piecerectangular frame having integral load bearing sections of substantiallyequal uniform cross-section extending along the frame edges betweenopposite parallel sides of the frame and permanently integrally joinedto one another at the frame corners over the entire cross-section ofeach section so as to provide a frame devoid of separable joints, saidframe containing a central rectangular test cavity and a rectangularopening in each side of said frame on the respective axis of saidcavity, whereby said frame has a pair of side openings on each of thethree axes of said cavity located in opposite parallel sides of saidframe; a pressurizing module at each frame side including a rectangularplate fitting snugly but removably within the respective frame opening,a rectangular diaphram at the inner side of said plate having edgeportions positioned between the plate edges and the wall edges of therespective frame opening and beads along said edge portions seating ingrooves in said plate edges for securing said diaphram to said plate influid sealing relation therewith to define between said diaphram andsaid plate a pressure chamber, and a port in said plate communicatingwith said chamber through which a pressure fluid may be introduced intosaid chamber to urge said diaphram against a test sample within saidcavity; and means releasably securing each module in its respectiveframe opening.